The stock stem should be 100mm ,so I would go to a 90mm or 85mm. Just buy a cheapy until you work out what length is good. That way you don't waste heaps of money if its not quite right.
Other option is to get yourself measured up and work it out from there.

I run a Thomson 90mm x 0 degree with Easton EA70 HiRise 2" rise bars. I love it, but I'd say you may want an 80-85mm x 10 degree to get you more upright. Or you may think about an 80-85mm with 2" rise bars.